Commutator cap construction



Au 15, 1950 c. A. ATWELL 2,519,217

COMMUTATOR CAP CONSTRUCTION Filed March 9, 1949 WITNESSES: INVENTOR Md 7? f CLARENCE A. ATWELL.

ATTORNEY Patented Aug. 15, 1950 2,519,217 YCOMMUTATOR CAP CONSTRUCTION Clarence A. Atwell, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania I Application March 9, 1949, Serial No. 80,386

2 Claims. 1

My invention relates to a molded insulating cap which fits over the front extension of the mica V-ring of the commutator of a dynamoelectric machine, such as a direct-current motor or generator. This frontextension of the mica V-ring has usually heretofore been protected, either by a string band, or by a molded cap such as is described and claimed in a Patent No. 2,400,- 968, granted to Norman I-I. Willby and myself on May 28, 1946.

The object of my present invention is to provide a protecting-cap construction which is a further improvement over that which is described in the aforesaid patent. In brief, my improved insulating cap has an integral rear flange-portion which protects the vulnerable front corner of the commutator where it comes in contact with the front extension of the mica V-ring.

In the accompanying drawing, the single figure shows a fragmentary longitudinal sectional View of a portion of a motor embodying my invention.

In the drawing, I have shown my invention applied to a commutator-type dynamo-electric machine in the form of a direct-current railway traction-motor, comprising a stator-member 3 and a rotor-member 4, the latter being mounted on a shaft and carrying a commutator-assembly 6 embodying my invention. The commutatorassembly is made up of a number of copper commutator-bars I separated by mica or other insulating bars 8, the two kinds of bars being of similar size and shape, except that the insulating bars are thinner and commonly project back about one-eighth of an inch behind the commutator-bars, as indicated by the numeral 8; that is, the mica bars 8 are longer than the copper bars i. The bars I and 8 are provided with V-grooves 9 in the ends thereof, said V-grooves having an inclined inner, arch-binding surface ll, usually at a 30 angle, and an outer surface l2, usually at 2. 3 angle, or sometimes a 6 angle.

The V-grooves 9 are insulatingly engaged by clamping V-rings l3 and !3 usually of steel, having conical surfaces inclined at the same angles as the surfaces of the V-grooves. The insulating engagement is provided through the intermediary of insulating V-rings l4, preferably made of sheet-mica of sufficient thickness to withstand the maximum voltage which is applied to the commutator-member.

At least the outer clamping V-ring it, or the one at the front end of the machine, has an outer conical surface l which extends out of the associated V-groove 9, beyond the end of the commutator-bars l. The corresponding insulating V-ring l4 likewise has an extended outer conical portion l6 which fits against the extended portion l5 of the clamping V-ring, and which preferably extends out substantially to the large end of the outer conical surface 15 of the clamping V-ring l3. It is this free or extended portion E5 of the insulating V-ring H! which was formerly held down by a string-band, or by the molded insulating cap which is described and claimed in the afore-mentioned patent.

The clamping-rings l3 and 13 are held in clamping-position by means of a nut ll applied to the ring 43 so as to hold the inner conical surface [8 of each clamping-ring in arch-binding clamping-engagement with the corresponding surface ll of the respective V-grooves.

The commutator-bars l are provided with armature-connections 20 which cause the commutator-bars to operate at such voltage as to involve the danger of fiashovers to ground, under operating conditions of the machine, particularly when the machine is utilized as a street-car or electric-locomotive motor which is operated close to the ground, in wet, dirty weather. Such flashovers may take the form of arcs from the free ends of one or more commutator-bars l, to any adjacent grounded surface, such as the end of the associated clamping V-ring 13, or, as shown,

\ I provide flashing-sectors 2! which are carried by the bearing-cartridge 22, between the brushholder-supporting structures 25 which support the brushholders 25 for carrying the brushes 21 which bear on the cylindrical surface of the commutator.

In accordance with my invention, the free, extending ends 15 of the mica V-rings M are held down, and at the same time the commutator is protected against flashings, by means of a rigid insulating cap 3! which is preferably molded of layers of impregnated asbestos-paper, so as to provide a rigid structure of sufficient mechanical strength to resist centrifugal forces. This cap 3'!) has a substantially cylindrical portion 31, which extends over said extending portion iii of the insulating V-ring I4. Preferably, this substantially cylindrical portion 3: is of such diameter that its inner surface is substantially in direct contact with the end-portion, or largest end, of the extended portion 96 of the insulating V-ring Id. The cap also has an integral front flange-portion 32 which extends down radially over the end of the associated clamping V-ring it.

The construction so far described is similar to that which is described and claimed in the afor said patent. Such a construction admirably ac- 

